This invention relates to duct units and other devices that can be connected to an air flow outlet of a machine having a rotating axial flow member, for example, a gas turbine and the invention further includes heat recovery apparatus.
The use of large gas turbines for generating electrical power is well known in the power generation art. These large gas turbines can be mounted horizontally in a building or other shelter that provides protection to the turbine against the elements. The outlet for the turbine, through which passes a hot air flow at substantial speed, can be connected to a diffuser duct of cylindrical configuration and then to a transition duct which transforms the hot air outlet passageway from a circular cross-section to a rectangular cross-section. A damper can then be provided, which damper in a first position can direct the hot air flow upwardly through a suitable outlet stack (also referred to as a by-pass stack) which can, in some cases, include some form of silencer arranged in a duct section in order to reduce the level of sound exiting from the stack. If the damper is moved to another position, the hot air can be directed through another pipe section to a heat recovery system, i.e. a heat recovery steam generator. The known heat recovery steam generators can be quite tall and they can include an exterior housing in which is mounted an array of heat exchanging units. Each heat exchanging unit can comprise a series of heat exchanging pipes through which a liquid such as water flows. The flowing water is heated by the hot exhaust gases from the turbine resulting in the generation of steam.
The known hot gas outlet arrangements designed for attachment to the outlet of a gas turbine of the aforementioned type suffer from several disadvantages and deficiencies. For example, the known outlet stack arrangements, even if they are provided with some form of duct silencer, are not very efficient at reducing the level of sound exiting from the gas turbine. One reason for this is that the silencer module, if it is provided at all, may be spaced a substantial distance from the outlet of the gas turbine sound reduction due to the transmission of sound through the walls of the ducts located upstream of the silencer. Also, if the diverter damper is directing the hot air flow into a heat recovery apparatus rather than straight through the by-pass stack, a silencer duct located along the path for the by-pass stack will be useless in reducing the amount of noise generated by the turbine and exiting from the hot air outlet system.
A further substantial difficulty with the known heat recovery apparatus used downstream from a gas turbine is that the hot air from the turbine is not directed evenly over the heat exchanging units which may be mounted in series in a tower-like housing. If the hot air is distributed unevenly, then this will result in uneven heating of the heat exchanging fluid flowing through the heat exchanging units, reducing the efficiency of the heat recovery for the steam generator. Also, uneven hot air distribution in the heat recovery apparatus can result in excessive pressure loss in this apparatus, reducing the gas turbine efficiency.
It is one object of the present invention to provide an improved sound attenuating duct unit suitable for connection to an air flow outlet of a rotating axial flow machine, such as a gas turbine, and able to provide a greater level of sound reduction than is achieved with existing known sound attenuating devices used in combination with such a machine.
It is a further object of the present invention to provide a new sound attenuating duct unit which employs sound attenuating members located between a diverter damper mounted in the duct housing and an air inlet of the duct unit.
It is another object of one aspect of this invention to simplify the silencer modules used in known by-pass stacks and main exhaust stacks, thereby achieving less pressure drop and reducing manufacturing costs.
It is a further object of the present invention to provide a heat recovery apparatus which includes a housing containing an array of heat exchanging units and a series of aerodynamic diffusers adjacent an inlet of the housing, the diffusers acting to redirect a substantial portion of incoming hot air in order that this hot air will pass more uniformly through the heat exchanging units.
It is another object of one aspect of the present invention to provide a new diverter section for a machine having a rotating axial flow member, this section capable of reducing greatly the pressure drop when air passes through it.